Heat oil in a large frying pan over medium-high heat.
Add mustard seeds, cumin seeds, dal (skinned black gram), dried red chilies, curry leaves, onions, green chilies, and ginger.
Saute, stirring, for about 2-3 minutes or until onions are soft.
Add tomatoes and asafoetida. Cook tomatoes, stirring occasionally, for about 3-4 minutes or until mushy.
Add flour slurry and water. Season with salt.
Bring to a boil. Simmer for about 5-7 minutes.
Add garam masala, ghee, and coriander leaves (cilantro). Heat through. Serve hot.
If the chutney becomes too thick, add a little hot water and stir. If it is too thin, continue simmering for another couple of minutes.
Serve as a side dish with dosa, roti, idli, and poori.